Systems and methods for electrospray using chromatographic columns with conducting or semiconducting stationary phases

Electrospray ionization (ESI) is a technique used in mass spectrometry (MS). More specifically, ESI is a “soft” ionization technique extensively used for production of gas phase ions with low levels of fragmentation. In a typical ESI process, a high voltage is applied to a liquid to create charged droplets which desolvate to form gas phase ions. Low flow electrospray, or “NanoESI,” produces charged droplets from an emitter having a relatively small inner diameter (e.g., approximately 20 micrometers or less). The combination of low flow rate and small diameter results in increased ionization efficiency (i.e., increased ratio of gas phase ions produced per available analyte molecules in solution) and allows for a reduction in the amount of sample required. When this emitter is positioned near a mass spectrometer inlet, which serves as a counter electrode, the gas phase ions produced are sampled into the instrument for mass analysis.

ESI is commonly used to couple the output of a chromatography column or system to mass spectrometry (MS). Chromatography techniques such as liquid chromatography (LC) can be used to create temporal separation between molecules in solution. The eluate can be fed to an electrospray emitter to serve as the input for the mass spectrometer.

Provided herein is an electrospray system. The electrospray system includes a first pre-column fluid junction to receive a fluid sample. The electrospray system includes a chromatographic column for separating analytes within the fluid sample. The chromatographic column includes a conductive or semi-conductive stationary phase disposed between a first end and a second end of the chromatographic column. The first end is fluidically connected to the first pre-column fluid junction. The electrospray system includes a post-column fluid union having a first fluid port and a second fluid port. The first fluid port receives separated analytes in the fluid sample from the second end of the chromatographic column. The electrospray system includes an electrospray emitter fluidically connected to the second fluid port. The electrospray system includes an electrical conductor connected to the post-column fluid union and the first pre-column fluid junction to equalize electrical potential between the post-column fluid union and the first pre-column fluid junction.

Provided herein is a method for reducing electro-chromatographic effects in an electrospray system. The method includes flowing a fluid sample from a first pre-column fluid junction to a first end of a chromatographic column. The chromatographic column includes a conductive or semi-conductive stationary phase disposed between the first end and a second end of the chromatographic column. The method includes separating analytes within the fluid sample using the chromatographic column. The method includes outputting the separated fluid sample from the second end of the chromatographic column to a first fluid port of a post-column fluid union The post-column fluid union has a second fluid port connected to an electrospray emitter. The method includes applying an equipotential voltage in a range of +1 to +10 kilovolts or in a range of −1 to −10 kilovolts at both the first pre-column fluid junction and at the post-column fluid union using an electrical conductor in electrical contact with the first pre-column fluid junction and the post-column fluid union.

Provided herein is a cartridge for insertion into an electrospray system. The cartridge includes a first pre-column fluid junction to receive a fluid sample The cartridge includes a chromatographic column for separating analytes within the fluid sample. The chromatographic column includes a conductive or semi-conductive stationary phase disposed between a first end and a second end of the chromatographic column. The first end is fluidically connected to the first pre-column fluid junction. The cartridge includes a post-column fluid union having a first fluid port and a second fluid port. The first fluid port receives separated analytes in the fluid sample from the second end of the chromatographic column. The cartridge includes an electrospray emitter fluidically connected to the second fluid port. The cartridge includes an electrical conductor connected to the post-column fluid union and the first pre-column fluid junction to equalize electrical potential between the post-column fluid union and the first pre-column fluid junction.

Systems, methods, and cartridges taught herein improve chromatographic performance in electrospray systems that feature a chromatographic column having stationary phase(s) formed of conductive or semi-conductive materials or substrates. In conventional electrospray systems, the electrical setup allows leakage currents to pass through the eluent. Such an arrangement is not suitable for use with a chromatographic column having a conductive or semiconductive stationary phase because current flow through such conductive columns causes charging of the column over time that subsequently generates adverse interactions with analytes during analyte separation in the column. Systems, methods, and cartridges taught herein overcome this problem by electrically connecting a fluid junction located upstream of the chromatographic column to a fluid union located downstream of the chromatographic column using an electrical conductor. The electrical conductor creates a high voltage equipotential between a first end of the chromatographic column and a second end of the chromatographic column that limits or eliminates current flow through the chromatographic column.

Systems, methods, and cartridges taught herein also enable measurement of electrospray current in systems using chromatographic columns having conductive or semi-conductive stationary phases while maintaining high chromatographic performance. In conventional systems, the current monitoring circuit is connected between a power supply and an electrospray emitter in such a way that slightly different voltages are applied to the ends (i.e., inlet and outlet) of the chromatographic column. In systems, methods, and cartridges taught herein, the electrical conductor that connects the fluid junction and the fluid union is connected in series with the current monitoring circuit. As such, no current flows through the chromatographic column having a conductive or semiconductive stationary phase but accurate measurement of the electrospray current is still enabled.

According to some embodiments taught herein, electrospray systems, methods, and cartridges taught herein enable improved chromatographic performance by including the fluid union as the only post-column fluidic connection. The chromatographic column creates temporal separation of analytes in solution, and analyte bands travel to the electrospray emitter. Each fluidic connection through which the analyte bands pass en route to the electrospray emitter can create disturbances to the laminar fluid flow (e.g., flow eddies). Additionally, unswept (no-flow) volumes are created at each fluidic connection within which the analytes diffuse (passive transport). Because this is a much slower process than active transport, a part of the analyte plug or band will lag behind the bulk of the plug causing a “tailed plug.” These processes impact the quality of the separation as they lead to dispersion of the analyte bands, or so called “band broadening”. In systems, methods, and cartridges taught herein, the use of the electrical conductor enables true equipotential between ends of the column while using only a single post-column fluidic connection (i.e., the fluid union). Thus, the systems and methods according to some embodiments herein can improve chromatographic performance (e.g., reducing peak broadening as compared to conventional systems and regulating retention time) by avoiding charging of the conductive or semiconductive stationary phase in the chromatographic column and limiting the number of post-column fluidic connections to one.

E E Accurate current-to-voltage curves (i.e., current flow through electrospray emitter as function of applied voltage) are important for characterizing, diagnosing, and optimizing an electrospray system. Such curves assist with differentiating between various electrospray regimes that principally govern the sensitivity of the instrumentation. In a first electrospray regime, the electrospray voltage (V) is below a threshold value with the result that the emitter emits no spray or dripping fluid. For example, the first electrospray regime can occur below 1,200 volts in some embodiments. A second electrospray regime occurs where the applied electrospray voltage (V) is sufficient to cause electrospray within the stable spindle regime where charged droplets are formed directly from a filament that extends from the Taylor cone. For example, the second regime can occur when the electrospray voltage is in a range from 1,200 to 2,200 volts. In a third regime, the applied electrospray voltage results in a cone jet where truncation of the filament is aided by coulombic repulsion thereby creating a diffuse plume of charged droplets. For example, the third regime can occur when the electrospray voltage is over 2,200 volts. The three electrospray regimes are characterized by abrupt changes in slope on a graph of spray current as a function of applied voltage. Embodiments of the present disclosure allow precise determination of spray current as function of applied voltage and so enable creation of such a graph. On the I-V graph, the inverse of slope (i.e., 1/slope) represents the effective impedance for given parameters such as flow rate, tip diameter, fluid composition, etc. This knowledge is important at least for setup, spray optimization, and diagnostics, and other methods to obtain the effective impedance (including processing images of the electrospray plume) are complicated and time-consuming. Thus, embodiments taught herein can enable improvement or optimization of the spray by direct measurement of the electrical properties without complex imaging algorithms or associated techniques.

Additionally, changes in the current-to-voltage characteristic for an electrospray system or cartridge are indicative of system or cartridge health. Thus, monitoring these characteristics with a controller can provide a diagnostic tool to assess system or cartridge health. One of the benefits of the electrical arrangement taught in embodiments describe herein is that the improved fidelity of the current measurement readback enables direct measurement and software automation of health and operation information for the electrospray system that would otherwise have to be obtained from an optical inspection apparatus of the ESI plume.

However, conventional systems and methods to measure the electrospray current have notable shortcomings, particularly for systems with chromatographic columns having a conductive or semiconductive stationary phase. Off-the-shelf power supplies, while most often outfitted with current and voltage monitor outputs, will only report the total load current. In reality, there are unknown leakage or spurious paths for current flow created by the conductive fluid streams themselves and by conductive elements in the fluidic path. To obtain an accurate measure of ESI current, other current flows must be either ignored or subtracted from the whole. This requires a separate independent measure of spray current which is not typically available by the high voltage supply manufacturer. Any other loads, whether intentional or unintentional, must also be accounted for. The problem is further compounded when considering that these extremely small currents (e.g., requiring greater than 10 nanoamps of precision) are measured in the presence of an extremely high common mode voltage. For the case of a ±8 kilovolt power supply, the measurement circuit typically uses a minimum common mode rejection on the order of 100 decibels or more. Additionally, tolerance matching of high voltage and high ohm resistors is needed to better than 0.01% accuracy.

Systems, methods, and cartridges taught herein enable accurate measurement of electrospray current in electrospray systems that include chromatographic columns having conductive or semiconductive stationary phases by using an electrical conductor in series with a current sensing circuit to create a voltage equipotential between the pre-column fluid junction located at a first end of the chromatographic column and a post-column fluid union located at a second end of the chromatographic column.

1 FIG. 1 FIG. 2 FIG. 3 FIG. 100 106 100 102 106 104 122 114 100 108 102 102 106 106 122 104 114 110 102 118 116 120 116 104 122 104 114 114 112 112 schematically illustrates a prior art electrospray systemincluding a chromatographic columnwith non-conductive stationary phase (e.g., packed polymer or glass beads). In,, andof this document, dashed line connections between components denote fluidic pathways while solid line connections between elements denote electrical pathways. The prior art electrospray systemincludes a fluid junction, the chromatographic columnhaving a non-conductive stationary phase, a post-column fluid union, a post-column fluid junction, and an electrospray emitter. A fluid sample is supplied to the electrospray systemfrom a liquid chromatography systemvia the fluid junction. The fluid sample travels from the pre-column fluid junctionthrough the chromatographic column. The chromatographic columntemporally separates analytes within the fluid sample and outputs a separated fluid sample (i.e., a fluid sample including separated analytes). The separated fluid sample flows to the post-column fluid junctionand then to post-column fluid unionbefore being emitted out through the electrospray emitter. A power supplyis connected to the fluid junctionand to a high sideof a current sensing circuit. A low sideof the current sensing circuitis connected to the fluid unionand the post-column fluid junction. When a sufficient voltage is applied at the fluid union, fluid at the electrospray emitteris ionized and forms a stream of droplets that are propelled from the electrospray emitterto a counter electrode. The counter electrodeand a negative terminal are connected to a common ground (which may be Earth ground in some cases). Thus, the flow of ionized droplets completes an electrical circuit and produces a measurable current flow.

112 110 112 In some embodiments, the counter electrodecould be floated at an offset voltage referenced to ground, the offset voltage being small (less than 200V) relative to the electrospray voltage from power supply. In some embodiments, an atmosphere-to-vacuum-inlet of a mass spectrometer can serve as the counter electrode. In embodiments that include a small float offset voltage, another ion optical element in the mass spectrometer can be held at ground (e.g., a c-trap) thereby allowing for ions to be guided by ion optical elements held at progressively lower (or higher, depending on their polarity) voltages.

1 FIG. 116 104 122 110 104 100 116 104 122 102 102 102 108 108 + In, the current sensing circuitis arranged in series with the fluid unionand the post-column fluid junctionand measures the current flowing from the power supplyto the fluid union. The conventional electrospray systemattempts to divert leakage currents out of the measurement path of the current sensing circuitby applying a common voltage to the fluid unionand the post-column fluid junctionwhile high voltage is applied to the fluid junction. In some instances, no voltage Vis applied at the fluid junction. If no voltage is applied to pre-column fluid junction, leakage current occurs as current flows through the conductive fluid stream to the grounded liquid chromatography system. In this application, “leakage current” refers to current from the power supply that does not travel to the electrospray emitter and counter electrode but, rather, travels along a separate path away from the emitter to ground (e.g., along a path through the fluid sample to upstream of the chromatographic column and to the grounded liquid chromatography system). Leakage current can prevent accurate measurement of the electrospray current if the leakage current is measured by the current sensing circuit but does not travel through the electrospray emitter to ground.

+ + E + E + 102 106 116 102 108 106 The application of the voltage Vat the fluid junctionis insufficient to eliminate leakage currents across the chromatographic columnbecause the voltage Vis not equal to the voltage Vthat is applied to the fluid union. The difference can arise due to a non-zero voltage drop across the current sensing circuitand other factors such as different contact resistances or material compositions of the fluid junction or the fluid union. Because of the very high voltages involved, even a small difference between Vand Vcan enable leakage current of the order of the spray current. The same issue of current leakage arises if the voltage Vis removed from the fluid junctionbecause current will then leak through to the grounded liquid chromatography system. However, these conventional systems include chromatographic columns with non-conductive stationary phases. A substantial voltage drop (up to thousands of volts) can exist across such chromatographic columnswithout impacting the performance of the chromatographic separation because the non-conductive stationary phase operates similarly whether it is in the presence or absence of current flow due to the voltage drop.

102 122 106 116 116 104 122 In other conventional schemes, the pre-column fluid junctionand the post-column fluid junctionare kept at ground potential (i.e., substantially zero volts). In such schemes, the stationary phase of the chromatographic columnis not subjected to current flow. However, such an arrangement is disfavored as it does not allow for accurate measurement of electrospray current alone using the current sensing circuitbecause the current sensing circuitwill measure both electrospray current and the leakage current that arises between the post-column fluid unionand the post-column fluid junction.

1 FIG. 4 FIG. 122 104 The setup ofcreates problems in use of a chromatographic column having a conductive or semiconductive stationary phase. Leakage current through a chromatographic column having a conductive or semiconductive stationary phase can induce charging that affects the flow and retention time of analytes within the column as taught in greater detail below with respect to. Performance degradation can occur with even a small voltage drop across the chromatographic column (e.g., a voltage drop as small as 10 V). Additionally, the presence of two liquid-metal interfaces (i.e., the post-column liquid junctionand the fluid union) creates two locations where flow perturbations can impair the quality of analyte separation in the separated fluid sample leaving the chromatographic column as each liquid-to-metal interface contributes to dispersion of the analyte bands, or so called “band broadening.”

The systems, methods, and cartridges taught herein mitigate these issues of leakage currents and band broadening by creating a true non-zero voltage equipotential (e.g., in a range of +1 kV and +10 kV or in a range of −1 kV and −10 kV) between the ends of a chromatographic column having a conductive or semiconductive stationary phase. Additionally, band broadening effects are mitigated because the systems taught herein reduce the number of post-column fluid junctions (e.g., fluid-metal interfaces) from two to one.

2 FIG. 2 FIG. 200 302 200 206 204 304 302 306 308 200 202 210 314 306 304 306 304 306 304 302 302 E illustrates a schematic view of an electrospray systemwith a chromatographic columnhaving a conductive or semiconductive stationary phase in accordance with some embodiments taught herein. In, the dashed line connections between components indicate fluidic connections while solid line connections between components indicate electrical connections. The fluidic components of the electrospray systeminclude a pre-column fluid junction(which can be a bulkhead fitting or other fluidic system inlet or interface in some instances), a pre-column fluid junction(which can be a needle seat or fluidic cartridge inlet or interface in some instances), a pre-column fluid junction(which can be an intra-cartridge fluidic junction in some instances), a chromatographic columnhaving a conductive or semiconductive stationary phase, a post-column fluid union, and an electrospray emitter. The electrospray systemalso can include electrical components such as a power supply, a current sensing circuit, and electrical conductors to electrically connect components to one another. In particular, an electrical conductorconnects the fluid unionand the fluid junctionto equalize the electrical potential between the fluid unionand the fluid junction. By applying an equal electrical potential (for example, the high electrical voltage potential Vemployed in electrospray emission) to both the fluid unionand the fluid junction, the possibilities for electrical current leakage and electrochemical interactions in the chromatographic columnare further reduced or eliminated while, at the same time, the chromatographic columncan be floated at a high electrical potential.

200 206 108 108 218 204 220 304 304 222 318 302 302 320 302 302 224 310 306 306 308 312 306 308 308 308 308 112 112 E 2 FIG. A fluid sample enters the electrospray systemthrough the pre-column liquid junction. The source of the fluid sample can be an external reservoir or external liquid chromatography system. In some examples, the external liquid chromatography systemis responsible for delivering the solvent, loading the sample, and running the gradient. The fluid sample flows along fluidic pathto the pre-column fluid junction. The fluid sample then flows along fluidic pathto the fluid junction. In embodiments where some components are assembled into a cartridge format (described in greater detail below), this is the point at which the fluid sample has entered the cartridge. The fluid sample flows from the fluid junctionalong fluidic pathto a first endof the chromatographic column. In the chromatographic column, analytes of the fluid sample are temporally separated within the fluid sample such that a separated fluid sample (i.e., a fluid sample including separated analytes) is output from a second endof the chromatographic column. For example, the chromatographic columncan be configured for, for example, liquid chromatography (LC) to separate molecules in a liquid mobile phase. The separated fluid sample is eluted from the chromatographic column and travels along a fluidic pathto a first fluid portof the fluid union. The fluid sample is ionized by a high electrical potential (V) applied at the fluid union. The electrospray emitteris connected to a second fluid portof the fluid union. The ionized fluid stream is emitted from the electrospray emitteras ionized droplets. For example, the electrospray emittercan include a needle and the droplet can be ejected through a distal tip of the needle. In some embodiments, the electrospray emitterhas an inner diameter of less than about 30 micrometers to enable nanoESI. In some embodiments, the emitted ionized droplets leave the electrospray emitterand travel towards an atmospheric pressure inlet to a mass spectrometer that serves as a counter electrode. The electrospray current return is commonly formed by the electrically grounded counter electrodeas shown in.

202 212 210 308 112 202 202 214 210 314 304 306 304 306 314 210 314 304 306 210 206 208 220 218 100 1 FIG. 1 FIG. The power supplyis electrically connected to a high sideof a current sensing circuitto measure the electrospray current arising from the flow of ionized droplets between the electrospray emitterand a counter electrode. In some embodiments, the power supplyoutputs a high voltage in a range of ±1 kV to ±10 kV. For example, the power supplymay output a voltage of ±2 kV or ±8 kV. The low sideof the current sensing circuitis connected to an electrical conductorthat further connects to the fluid junctionand the fluid union. In other words, the fluid junctionand the fluid unionare electrically connected in parallel with one another through the electrical conductor, and this parallel circuit is connected in series with the current sensing circuit. Thus, the electrical conductorcreates a true equipotential between the fluid junctionand the fluid unionas there are no intervening elements between the two (such as the current sensing circuit) to create a difference in potential. In essence, the two pre-column fluid junctionsandform a pre-column voltage spacer that directs current around the chromatographic column to prevent current flow through the chromatographic column. As a consequence of employing the pre-column voltage spacer, a small amount of voltage is dropped across the fluidic linewhile the majority of the voltage drop occurs along fluidic line. The use of a pre-column voltage spacer can be contrasted with the post-column voltage spacer arrangement in the conventional electrospray systemofwherein improvement in the electrospray current measurement is accompanied by a small voltage drop across the conductive or semi-conductive stationary phase of the chromatographic column that can lead to undesirable charging effects that impact retention time. The post-column voltage spacer ofalso negatively induces band broadening due to the presence of two liquid-to-metal interfaces.

314 306 314 304 314 In some embodiments, a lead of the electrical conductoris connected directly to an outer conductive surface of the fluid unionto provide electrical current to the fluid stream sufficient to provide ionization therein. In some embodiments, a lead of the electrical conductoris connected directly to an outer conductive surface of the fluid junction. In some embodiments, the electrical conductorcan include an electrical wire or cable and can include shielding or be a bare conductor.

202 200 202 200 202 202 112 202 210 Note that the power supplycan be supplied with the electrospray systemin some embodiments as a combined system. In other embodiments, the power supplyis not provided as part of the system but, rather, the electrospray systemis designed to interface with a power supplythat is provided separately. In some embodiments, the polarity of the power supplyis reversed such that high voltage is applied to the counter electrodeand the return voltage lead of the power supplyis connected to the current sensing circuit.

308 210 212 214 306 304 216 208 + E E NanoESI plumes typically carry between 50 to 500 nano Amperes of current. As such, because nanoESI results in greater sensitivity and produces relatively small ion currents, measurements are made of these small ion currents to 10 nano Amperes or better of measurement resolution as it is highly desirable to measure the electrospray current to a high degree of accuracy to ensure that the electrospray emitteris operating in the correct electrospray regime. Because a voltage drop occurs across the current sensing circuit, the voltage Vat the high sidedoes not match the voltage Vat the low side. The voltage Vis applied in parallel at the fluid unionand the fluid junction. In some embodiments, the electrical connectors pass through a high-voltage electrical connectorthat can be mounted, for example, on a housing of the cartridge.

108 206 112 202 The liquid chromatography system, pre-column fluid junction(e.g., system inlet), counter electrode, and negative terminal of the power supplyare connected to electrical ground. It should be understood that “electrically grounded” as used herein may also include electrical potentials operated at or near electrical grounds, or substantial electrical grounds. For example, in some instances, the electrical grounds may be biased up to +/−150 volts, which when compared to the +/−2 to 10 kilovolts of common mode voltage taught herein, represents a substantially grounded source.

302 302 302 302 318 320 302 302 −2 2 The chromatographic columnincludes conductive or semi-conductive materials or substrates that form and/or support the stationary phase. For example, the stationary phase of the chromatographic columncan include (or be formed of) silicon, gallium arsenide, gallium nitride, indium tin oxide, n-type or p-type semiconductor materials, or doped semiconductors. In other embodiments, the stationary phase of the chromatographic columncan include conductive metals such as platinum or stainless steel. In some embodiments, the stationary phase of the chromatographic columnincludes or is supported by a conductive or semi-conductive substrate that is disposed between a first endand a second endof the chromatographic column. In some embodiments, the chromatographic columncan have a resistivity in a range from 1×10Ω·cm to 1×10Ω·cm.

302 300 304 306 304 318 302 222 306 320 302 224 302 In some embodiments, the chromatographic columncan include microfabricated structural features such as pillars extending from a substrate within a microfluidic flow channel. The microfluidic structural features include a conductive or semi-conductive material such as silicon and can be generated using micro- or nano-fabrication techniques known to one of ordinary skill in the art including, for example, using photo- or electron-beam lithography and deep reactive ion etching. The pillars form the stationary phase of the chromatographic column. In some examples, the pillars or other microfluidic structural features are formed from a silicon substrate by etching voids surrounding the pillars. Examples of devices appropriate for use as chromatographic columns in embodiments taught herein are described in U.S. Patent Application Publication No. 2016/0001199, the entire contents of which is incorporated herein by reference. In some embodiments, microfluidic columns consist of rectangular channels that have been etched into microfluidic chips (e.g., semiconductor chips or substrates) using deep reactive etching technology. Certain features of the electrospray system, such as the pre-column fluid junctionand/or the post-column fluid union, can also be integrated directly onto the microfluidic chip. In some instances, the fluid junctioncan be located on-chip directly adjacent to the first endof the chromatographic columnthus reducing or eliminating the fluidic path. In some instances, the fluid unioncan be located on-chip directly adjacent to the second endof the chromatographic columnthus reducing or eliminating the fluidic path. In some embodiments, silanols in the conductive or semiconductive stationary phase of the chromatographic columnare chemically end-capped so that secondary (e.g., electrochemical) interactions with analytes are reduced. Similarly, the outer layer of the conductive or semiconductive stationary phase of some examples can be chemically treated to form a layer of a different material, such as by changing silicon into silicon oxide, or can be coated with thin layers of other materials to reduce analyte interactions. As opposed to chromatographic columns with non-conductive stationary phases, which usually include a heterogeneously packed bed of functionalized spherical particles (e.g., fused silica particles) as stationary phase, the bed in conductive or semiconductive microfluidic/microfabricated chromatographic columns is formed by etching pillars located at uniform distances. Compared to packed bed columns, microfluidic chromatographic columns offer several advantages. First, peak dispersion originating from heterogenous flow paths across the column cross-section (e.g., eddy dispersion), which arises in heterogeneous packed-bed columns, is reduced in chromatographic columns having microfabricated or deep reactive ion etched features such as pillars due to the homogeneous spacing between features. Second, column permeability is increased. Finally, the homogeneity of microfabricated chromatographic columns creates excellent column-to-column reproducibility.

302 In other embodiments, the chromatographic columncan include other conductive or semi-conductive stationary phase materials such as porous graphitic carbon beads.

122 104 302 122 314 210 200 306 1 FIG. The use of chromatographic columns with conductive or semiconductive stationary phases in conjunction with electrospray emitters has been limited by issues that arise due to electrical conductivity of the stationary phase. For example, doped semiconductor substrates and materials (e.g., a boron-doped semiconductor) include impurities that create holes (unoccupied electron states), making it an electron acceptor. The substrates do not conduct these holes well, leading to an accumulation of charges. In effect, current flow through the chromatographic column can cause charging of the stationary phase in the chromatographic column that, in turn, interacts with the analytes during the separation. Similarly, having a voltage difference between the first end and the second end of the chromatographic column can generate electrochemically induced changes in the pH of the solvents in the fluid sample that eventually affect the stationary phase of the chromatographic column to worsen chromatographic outcomes. In addition, potential differences between the fluid sample and the chromatographic column, or between parts of the chromatographic column, can promote unwanted electrochemistry such as oxidation or reduction of solvent or analyte species in the fluid sample. These electrical issues are magnified at high voltages (i.e., kilovolts) because leakage currents are harder to ignore (become less negligible) under high voltage conditions. In some conventional systems, these disadvantages have been mitigated by effectively grounding the chromatographic column by introducing the additional post-column fluid junctionbetween the post-column fluid unionand the second end of the chromatographic columnas shown in. The additional post-column fluid junction can be electrically grounded thus preventing current flow into the chromatographic column. However, each liquid-to-metal interface in the system downstream of the chromatographic column introduces additional dispersion in the chromatography peaks (i.e., undoes the work of the chromatographic column to separate analytes from one other). Thus, the additional post-column fluid junctionof the conventional system introduces additional peak dispersion. The use of an electrical conductoras taught herein to equilibrate electrical potential across the chromatographic column resolves these issues while still enabling floating of the chromatographic column at high voltage and enabling high resolution measurement (e.g., to nanoamp levels) of the electrospray current by the current sensing circuit. Additionally, the only post-column liquid-to-metal interfaces in electrospray systemoccur at the fluid unionwhere electrospray is initiated, thus reducing peak dispersion in the fluid sample.

208 208 208 208 200 208 204 218 208 200 204 218 200 210 314 216 208 210 216 208 208 208 In some embodiments, the fluidic or electrical components can be housed within a cartridge. As used herein, “housed” within the cartridge indicates that the component is mounted at least partially within the cartridge although some elements may extend out of the outer housing or casing of the cartridge. In some embodiments, use of a cartridge format can, in some cases, make expert-level liquid-chromatography mass spectrometry (LCMS) performance easier to attain by integrating the column and emitter into a cartridge format that also contains nebulization gas for consistent desolvation, an integrated heater for optimal chromatography, and on-board memory enabling use as a “smart consumable.” The integrated heater can provide thermal stability and reduce the level of backpressure needed to achieve suitable results. In some microfluidic and/or cartridge-based examples, the integrated heater is particularly useful for reducing the backpressure as components of the cartridgemay have lower pressure limits than would be achieved by a state-of-the-art liquid chromatography pump. For example, components of the cartridgesuch as the chromatography column may have a backpressure limit of 450 bar, and the integrated heater enables good performance even at the lower backpressure limit. The cartridgecan be a removable and replaceable component that is inserted or withdrawn from the electrospray systemin some embodiments. For example, the removable or replaceable cartridgecan be inserted into a receiving slot in a system housing. Insertion of the cartridge can facilitate fluidic connection between the pre-column fluid junctionand fluidic path, while removal of the removable cartridgefrom the electrospray systemcan facilitate breaking of the fluidic connection between the pre-column fluid junctionand the fluidic path. Similarly, insertion of the cartridge into the electrospray systemcan facilitate electrical connection of the low side of the current sensing circuitto the electrical conductorthrough the high-voltage electrical connectorwhile removal of the cartridgefrom the system can facilitate disengagement or breaking of the electrical contact between the current sensing circuitand the high-voltage electrical connector. In some embodiments, the housing or casing of the cartridgeis formed of non-conductive materials. In some embodiments, the cartridgeis sealed or sealable to prevent user contact with high voltages present inside the cartridgeduring operation and improve safe handling of the cartridge.

304 306 208 304 306 208 314 Placement of the fluid junctionand fluid unionwithin the cartridgecan advantageously provide additional electrical shielding of these components to ensure that voltage equipotential conditions are maintained and to improve safety by preventing users from coming into physical contact with high voltages. Even small resistivity differences along the electrical connections due to differences in electrical cables, electrical contact points, condition of fluidic unions and junctions, and fluidic union or junction surface states such as amount of oxidation on the surface can generate measurable leakage currents that can impact chromatography performance. Placement of the fluid junctionand fluid unionwithin the cartridgecan prevent subsequent movement of these fluidic parts as pressurized fluid samples are transmitted through them, thus ensuring improved electrical contact between the electrical conductorand these components.

2 FIG. 210 208 210 208 210 216 314 202 212 210 216 214 210 314 216 illustrates the current sensing circuitas being outside of the cartridge. However, it is also contemplated that the current sensing circuitcould be located within the cartridge. In such an embodiment, the current sensing circuitis placed in series between the high-voltage electrical connectorand the electrical conductor. For example, the power supplyand the high sideof the current sensing circuitcan connect through the high-voltage electrical connectorand the low sideof the current sensing circuitcan connect directly to the electrical conductorwithout the intervening high-voltage electrical connector.

204 204 304 304 304 306 304 306 304 306 The pre-column fluid junctioncan have an inner diameter in a range from 50 microns to 500 microns in some embodiments. In an example embodiment, the pre-column fluid junctioncan have an inner diameter of 280 microns. In some embodiments, the fluid junctioncan include one or more conductive materials. For example, the fluid junctioncan include a noble metal or stainless steel. In some embodiments, the fluid junctionor fluid unioncan include multi-port plumbing fixtures or fittings known to those in the art. In some embodiments, the fluid junctionand fluid unionare identical parts in terms of material composition, shape, or both material composition and shape. In practical implementations, different electrical and fluidic connections can give rise to different resistivities. By using identical material or identical shaped parts for the fluid junctionand fluid union, differences in contact resistance may be reduced. Unwanted ground currents can arise within the system such as through the housing. In some embodiments, the housing is formed of a non-conductive material.

204 304 220 E In some embodiments, the pre-column fluid junctionand the fluid junctioncan be merged into a combined fluid junction. In such embodiments, the fluidic pathis eliminated and the combined fluid junction is held at the emitter voltage V.

306 306 306 306 310 312 306 306 302 314 306 304 2 FIG. 3 FIG. In some embodiments, the fluid unioncan include one or more conductive materials. For example, the fluid unioncan include stainless steel. The fluid unionas depicted inandis a two-port device (i.e., the fluid unionincludes a first fluid portand a second fluid port). However, it may be desirable in LC-MS procedures to add certain chemicals to the mobile phase or introduce certain chemicals to the separated fluid sample after it leaves the chromatographic column but prior to electrospray emission to influence analyte ionization in order to improve analyte signal. Alternatively, some additives may be used to suppress unwanted signals or selectively enhance the signal of particular compounds in a mixture. As such, in some configurations, the fluid unioncan comprise additional fluid ports (e.g., third fluid port, fourth fluid port, and so on) to receive additional fluid streams (e.g., a second fluid, third fluid, and so on) that mix in the fluid unionwith the fluid sample received from the chromatographic column. In various embodiments, the additional fluid streams can each be sourced from separate reservoirs or from additional fluid columns such as additional chromatographic columns. In embodiments where additional fluid streams are received at additional fluid ports of the fluid union from additional chromatographic columns, the electrical conductorcan be extended to connect to additional fluid junctions upstream of the additional chromatographic columns. As such, an equipotential can be established between the fluid union, the fluid junction, and these additional fluid junctions. The additional fluid streams can include post-column additives in some embodiments. Post-column additives (PCAs) may be used to influence the electrospray ionization process in various ways, for example, to promote desolvation, change the charge state distribution, or other known ways, and they can be solvents or other chemical moieties.

218 220 222 224 218 220 222 224 218 220 222 224 218 218 218 218 220 220 220 220 In various embodiments taught herein, the fluidic paths,,,are formed of flexible or rigid tubing. In some embodiments, the fluidic paths,,,can include paths or capillaries formed at least in part of fused silica or plastic/polymeric materials. The fluidic paths,,,can include capillaries having inner coatings such as polyether ether ketone (PEEK). In some embodiments, the fluidic pathcan have an inner diameter in a range from 10 to 50 microns or in a range from 20 to 40 microns. The fluidic pathcan have an inner diameter of 30 microns in some embodiments. The fluidic pathcan have a length in a range from 10-50 cm or in a range from 20-40 cm. The fluidic pathcan have a length of 35 cm in some embodiments. In some embodiments, the fluidic pathcan have an inner diameter in a range from 10 to 50 microns or in a range from 20 to 40 microns. The fluidic pathcan have an inner diameter of 30 microns in some embodiments. The fluidic pathcan have a length in a range from 10-50 mm or in a range from 20-40 mm or in a range from 50-100 mm. The fluidic pathcan have a length of 35 mm in some embodiments.

222 222 222 222 224 224 224 224 224 224 218 220 In some embodiments, the fluidic pathcan have an inner diameter in a range from 5-50 microns. The fluidic pathcan have an inner diameter of 5 microns, 10 microns, 20 microns, 25 microns, 30 microns, or 40 microns in some embodiments. The fluidic pathcan have a length in a range from 10-50 mm or in a range from 20-40 mm or in a range from 50-100 mm. The fluidic pathcan have a length of 35 mm in some embodiments. In some embodiments, the fluidic pathcan have an inner diameter in a range from 5-50 microns. The fluidic pathcan have an inner diameter of 5 microns, 10 microns, 20 microns, 25 microns, 30 microns, or 40 microns in some embodiments. The fluidic pathcan have a length in a range from 10-50 mm or in a range from 20-40 mm or in a range from 50-100 mm. The fluidic pathcan have a length of 35 mm in some embodiments. The fluidic pathcan have a reduced inner and outer diameter as compared to other fluidic paths in the system to help reduce peak broadening. In one example, the fluidic pathhas an inner diameter of 5 or 10 microns while the fluidic paths,have an inner diameter of 30 microns.

310 312 306 306 208 308 306 222 224 318 320 302 106 In some embodiments, the cartridge (more specifically, a same chromatographic column and electrospray emitter) can be used for several hundred injections. However, a given chromatographic column tends to have a longer useful lifespan than a given electrospray emitter. Therefore, in some embodiments, the first fluid port, the second fluid port, or both the first and second fluid ports of the fluid unionare configured to enable disconnection and reconnection of fluidic paths or electrospray emitters attached thereto. In such embodiments, the electrospray emitter (or fluid union) can be removed from the cartridgeand replaced by a new electrospray emitteror fluid union. This ability to exchange the emitter enables the full use of the column's lifetime. In some embodiments, the fluidic pathand fluidic pathare configured to be disconnected and reconnected to the first endand the second endof the chromatographic column, respectively. By having removable fluidic paths, the chromatographic columncan be removed from the cartridge and replaced.

3 FIG. 300 302 300 302 318 320 306 304 308 306 304 314 306 304 314 318 320 302 depicts an electrospray systemwith a chromatographic columnhaving a conductive or semiconductive stationary phase in accordance with some embodiments taught herein. The electrospray systemincludes a chromatographic columnhaving a first endand a second end, a post-column fluid union, a pre-column fluid junction, and an electrospray emitter. The post-column fluid unionand the pre-column fluid junctionare connected by an electrical conductor. The electrical connection of the fluid unionto the fluid junctionby the electrical conductorcreates a true equipotential between the first endand the second endof the chromatographic column.

300 316 304 322 322 202 316 316 304 222 318 302 302 320 302 224 310 306 306 308 312 306 308 308 308 308 112 112 + 3 FIG. In some embodiments, the electrospray systemcan include a housing that shields and protects components within the housing. In some embodiments, the housing can be shaped as a cartridge that can be removably inserted into a larger system. The housing can include an inlet portfor fluid that is connected to the fluid junction. The housing can also include a high-voltage electrical connectormounted thereon or passing therethrough. A voltage can be applied to the high-voltage electrical connectorusing a power supply. A fluid sample is supplied to the inlet portfrom a fluid source. The fluid sample passes through the inlet portand a body of the fluid junctionalong fluidic pathto the first endof the chromatographic column. In the chromatographic column, analytes of the fluid sample are temporally separated within the fluid sample such that a separated fluid sample (i.e., a fluid sample including separated analytes) is output from the second endof the chromatographic column. The separated fluid sample travels along a fluidic pathto a first fluid portof the fluid union. The fluid sample is ionized by a high electrical potential (V) applied at the fluid union. The electrospray emitteris connected to a second fluid portof the fluid union. The ionized fluid stream is emitted from the electrospray emitteras ionized droplets. For example, the electrospray emittercan include a needle and the droplet can be ejected through a distal tip of the needle. In some embodiments, the electrospray emitterhas an inner diameter of less than about 30 micrometers to enable nanoESI. In some embodiments, the emitted ionized droplets leave the electrospray emitterand travel towards an atmospheric pressure inlet to a mass spectrometer that serves as a counter electrode. The electrospray current return is commonly formed by the electrically grounded counter electrodeas shown in.

300 202 304 306 202 322 202 300 300 202 + + 2 FIG. 5 FIG. 6 FIG. In the absence of a current sensing circuit, the electrospray systemcan receive the high voltage Vfrom the power supplyand distribute the high voltage Vdirectly to the fluid junctionand the fluid unionvia the electrical conductor. In other embodiments, a current sensing circuit similar to that described in relation to,, and/orcan be placed into the circuit between the power supplyand the high-voltage electrical connector. Note that the power supplycan be supplied with the electrospray systemin some embodiments as a combined system. In other embodiments, the electrospray systemis designed to interface with a power supplythat is provided separately.

4 FIG. 1 FIG. 1 FIG. 302 100 116 106 100 shows a graph of retention time for a particular analyte (specifically, a peptide with the amino acid sequence GLILVGGYGTR) in a chromatographic columnhaving a semiconductive stationary phase according to some embodiments taught herein for a series of replicated experiments under different conditions. These experiments demonstrate the effect on analyte retention time of charging due to non-equipotential voltage conditions on the chromatographic column having a conductive or semiconductive stationary phase. Note that voltage differences (or drops) of tens of volts across the chromatographic column can easily arise, e.g., in the electrospray systemofbecause of the high voltages being applied to the emitter (e.g., up to 8 kV). For example, for a current sensing resistor with a resistance of 10 MΩ and an electrospray current of 5 μA, a 50 V difference arises across the current sensing circuitand, hence, the chromatographic columnfor the electrospray systemshown in.

402 404 302 402 404 Under a first condition, the chromatographic column is grounded (i.e., the chromatographic column is isolated from the high voltage applied to the electrospray emitter by a grounded fluid junction placed between the emitter and the column). Under the second condition, the chromatographic columnis floated at high voltage (i.e., voltage sufficient to induce electrospray ionization of a fluid sample) with equipotential conditions between the first end and the second end of the chromatographic column as taught in various embodiments taught herein. As described above, the systems taught herein can achieve a float of the chromatographic column without the use of a second fluid junction downstream of the chromatographic column, which induces peak dispersion. Across both the first conditionand the second condition, the average retention time is relative stable and does not evolve or change over replicated experiments.

406 408 410 102 104 318 320 302 100 1 FIG. 4 FIG. Under the third condition, fourth condition, and fifth condition, voltage differences of +1.6 V, +9.6 V, and +19.2 V are intentionally induced between fluid junctions/unions (e.g., fluid junctionand fluid unionof the system of) located respectively at the first endand the second endof the chromatographic columnas would arise in a conventional system such as electrospray system. As seen in, the stability of the analyte retention time degrades significantly over repeated experiments due to charge accumulation in the semiconductive stationary phase of the chromatographic column. As a result, experimental results from early runs in an experimental series can no longer reliably be compared to experimental results from later runs in the experimental series.

410 302 404 302 318 320 300 304 306 302 412 318 320 302 302 After the application of the fifth conditionto the chromatographic column, the experimental condition was returned to the second conditionwherein the chromatographic columnis floated at high voltage with equal voltages applied to the first endand the second end(e.g., as occurs in electrospray systemwherein equal voltages are applied to fluid junctionand fluid union). It is seen that the retention time repeatability recovers over some early experimental runs to return to a stable retention time as further experimental runs are conducted. Finally, the chromatographic columnis subjected to a sixth conditionwhere an intentional voltage difference of −19.2 V is applied between the first endand the second endof the chromatographic column. Again, the retention time becomes unstable and changes from experiment to experiment as accumulated charge within the semiconductive chromatographic columnbegins to impact analyte retention within the chromatographic column.

4 FIG. Table 1 below gives the measured coefficient of variation for each of the experimental conditions illustrated in. As shown by the values, the experimental variation is significantly reduced under conditions where the first end and the second end of the chromatographic column are at equal electrical potentials.

Experimental Configuration Retention Time % CV first condition 402 0.10% second condition 404 0.08% third condition 406 0.13% fourth condition 408 0.51% fifth condition 410 0.54% repeated second condition 404 0.12% (last 10 injections once stable) sixth condition 412 0.25%

5 FIG. 5 FIG. 210 210 510 212 214 210 210 510 212 210 214 210 210 illustrates an example current sensing circuitfor use with embodiments of the systems, methods, and cartridges taught herein. The current sensing circuitcan include a current sensing resistordisposed between the high sideand the low sideof the current sensing circuit. In some embodiments, the current sensing circuitconsists only of the current sensing resistor, a first electrical lead connecting the high sideof the current sensing circuitto a voltmeter, and a second electrical lead connecting the low sideof the current sensing circuitto the voltmeter. In such an arrangement, the voltmeter can measure high voltages with high precision. To reduce the expense of the current sensing circuit, additional electronic elements such as those shown incan be used to attenuate the voltage levels such that data acquisition electronics compatible with modern computing devices can be used.

5 FIG. 210 510 502 504 506 212 214 510 502 504 502 504 502 504 506 514 210 510 In the embodiment shown in, the current sensing circuitincludes a current sensing resistor, a first voltage divider, a second voltage divider, and a difference amplifier. The voltage between the high sideand the low sideof the current sensing resistoris heavily attenuated via the precision voltage dividers (,) to comply with typical data acquisition and computer voltage potentials. In one embodiment, the precision voltage dividers,operate at a 1,000:1 reduction ratio. The resulting voltages at the outputs of the voltage dividers,can be subtracted using the difference amplifier. The difference obtained at an outputof the current sensing circuitprovides a direct proportional measure of the ESI spray current. In various embodiments, the resistance of the current sensing resistorcan be in a range from 10 kΩ to 10 GΩ, in a range from 1 MΩ to 1 GΩ, or in a range from 10 MΩ to 100 MΩ.

508 514 210 508 514 514 508 Optionally, a controllercan be coupled with the outputof the current sensing circuit. The controllermay be configured to receive the output current directly from outputor a digitized representation of the output. In some embodiments, the controllerdetermines a state of the electrospray emitter based on the measured electrical current flow. Specifically, the state of the electrospray emitter includes a mode of operation within a particular electrospray regime.

508 512 508 508 208 508 208 208 302 308 In some embodiments, the controllerincludes a user interfaceconfigured to display or otherwise alert a user or operator of the determined electrospray regime. In other embodiments, the controllercan interface with an external user interface. In some embodiments, the controllercan determine a health of the cartridge, for example, by tracking and identifying changes in the output current with respect to the applied voltage over time. If the changes are significant (e.g., past a threshold limit), the controllercan indicate to a user that the cartridge, or a portion of the cartridgesuch as the chromatographic columnor the electrospray emitter, should be replaced.

210 112 202 5 FIG. In the current sensing circuitof, the current measurement is obtained with high precision using relatively less expensive electronics without an isolation amplifier. One difficulty with direct high-side measurement techniques (i.e., measurement of electrospray current at the high voltage side of the circuit as opposed to low-side measurement of the return current from the counter electrodeto the power supply) is measuring current to nanoamp resolution in the presence of a very high common mode voltage (e.g., +/−8 kilovolts). Such a high common mode voltage is then heavily attenuated in order to protect the downstream electronics. Another solution to overcome these difficulties is by isolating, or electrically floating, the large common mode supply voltage and sense circuit to protect the downstream electronics. The measured quantity may be translated across the isolation barrier using modulation and demodulation techniques to the downstream electronics.

6 FIG. 5 FIG. 6 FIG. 210 210 510 212 214 210 602 604 602 604 606 606 608 608 514 210 508 210 202 schematically depicts an alternative current sensing circuitas an isolation amplifier circuit that is suitable for use in some embodiments taught herein. The isolation amplifier circuit can electrically float the large input voltage. In this embodiment, the current sensing circuitincludes the current sensing resistor. The high sideand the low sideof the current sensing circuitare electrically coupled with a first bufferand a second buffer, respectively. The outputs from the first bufferand the second bufferare connected to a difference amplifier. The output of the difference amplifierflows to an isolation amplifier. The output of the isolation amplifierforms the outputof the current sensing circuitthat may, optionally, be connected to a controlleras described above with respect to. The current sensing circuitdescribed inalso benefits from use of an isolated power supplyfor the floating amplifiers as well as a means of modulation and demodulation across the isolation barrier (not shown). The modulation and demodulation may introduce systematic noise.

Other embodiments of current sensing circuits and current monitoring circuits that are suitable for use with embodiments of systems, methods, and cartridges taught herein are described in U.S. Patent Application Publication No. 2023/0030920 by Lindseth et al., the entire contents of which is incorporated herein by reference.

7 FIG. 700 702 700 304 318 302 302 318 320 704 700 302 706 700 310 306 306 312 308 708 700 304 306 314 710 700 212 210 202 712 700 214 210 314 illustrates a routinefor reducing electro-chromatographic effects in an electrospray system, in accordance with various embodiments taught herein. In block, routineflows a fluid sample from a first pre-column fluid junctionto a first endof a chromatographic column. The chromatographic columnincludes a conductive or semi-conductive stationary phase disposed between the first endand the second endof the chromatographic column. In block, routineseparates analytes within the fluid sample using the chromatographic column. In block, routineoutputs the separated fluid sample from the second end of the chromatographic column to a first fluid portof the post-column fluid union. The fluid unionhas a second fluid portconnected to an electrospray emitter. In block, routineapplies an equipotential voltage in a range of +1 to +10 kilovolts or in a range of −1 to −10 kilovolts at both the first pre-column fluid junctionand at the post-column fluid unionusing an electrical conductorin electrical contact with the first pre-column fluid junction and the post-column fluid union. In optional block, the routineapplies a first voltage to the high sideof the current sensing circuitusing the power supply. In optional block, the routinetransmits the equipotential voltage from the low sideof the current sensing circuitto the electrical conductor.

208 2 FIG. Many of the embodiments taught herein are in the context of a replaceable ESI cartridge (e.g., cartridgein). However, the techniques taught herein can also be implemented in other systems that do not include the cartridge. In such embodiments without the cartridge, the system still advantageously provides speed and simplicity in replacing the electrospray emitter (e.g., by disconnecting the needle from the fluid union) without disturbing or otherwise dismantling the remaining fluid and electrical connections in the system.

Although the present systems, methods, and cartridges and associated advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments taught herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

The section headings used herein are for organizational purposes and are not to be construed as limiting the described subject matter in any way.

In this detailed description of the various embodiments, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the embodiments disclosed. One skilled in the art will appreciate, however, that these various embodiments may be practiced with or without these specific details. In other instances, structures and devices are shown in block diagram form. Furthermore, one skilled in the art can readily appreciate that the specific sequences in which methods are presented and performed are illustrative and it is contemplated that the sequences can be varied (unless explicitly noted otherwise) and still remain within the spirit and scope of the various embodiments disclosed herein.

All literature and similar materials cited in this application, including but not limited to, patents, patent applications, articles, books, treatises, and internet web pages are expressly incorporated by reference in their entirety for any purpose. Unless described otherwise, all technical and scientific terms used herein have a meaning as is commonly understood by one of ordinary skill in the art to which the various embodiments taught herein belongs.

It will be appreciated that there is an implied “about” prior to specific temperatures, concentrations, times, pressures, flow rates, cross-sectional areas, etc. discussed in the present teachings, such that slight and insubstantial deviations are within the scope of the present teachings. In this application, the use of the singular includes the plural unless specifically stated otherwise. Also, the use of “comprise”, “comprises”, “comprising”, “contain”, “contains”, “containing”, “include”, “includes”, and “including” are not intended to be limiting. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present teachings.

As used herein, “a” or “an” also may refer to “at least one” or “one or more.” Also, the use of “or” is inclusive, such that the phrase “A or B” is true when “A” is true, “B” is true, or both “A” and “B” are true. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

A “system” sets forth a set of components, real or abstract, comprising a whole where each component interacts with or is related to at least one other component within the whole.

Example 1. An electrospray system, comprising: a first pre-column fluid junction to receive a fluid sample; a chromatographic column for separating analytes within the fluid sample, the chromatographic column including conductive or semi-conductive stationary phase disposed between a first end and a second end of the chromatographic column, the first end fluidically connected to the first pre-column fluid junction; a post-column fluid union having a first fluid port and a second fluid port, the first fluid port receiving separated analytes in the fluid sample from the second end of the chromatographic column; an electrospray emitter fluidically connected to the second fluid port; and an electrical conductor connected to the post-column fluid union and the first pre-column fluid junction to equalize electrical potential between the post-column fluid union and the first pre-column fluid junction. Example 2. The electrospray system of example 1, further comprising a current sensing circuit having a high side and a low side, the low side of the current sensing circuit being electrically connected to the electrical conductor. Example 3. The electrospray system of example 2, further comprising a power supply electrically connected to the high side of the current sensing circuit. Example 4. The electrospray system of example 3, further comprising a second pre-column fluid junction to deliver the fluid sample to the first pre-column fluid junction, wherein the power supply is electrically connected to supply high voltage to the second pre-column fluid junction. Example 5. The electrospray system of example 1, wherein the post-column fluid union and the first pre-column fluid junction are electrically connected in parallel with one another and in series with a current sensing circuit. Example 6. The electrospray system of example 1, wherein a fluidic path connecting the second end of the chromatographic column and the post-column fluid union has an inner diameter of 30 micrometers or less to reduce peak broadening. Example 7. The electrospray system of example 1, wherein the chromatographic column, the post-column fluid union, the electrospray emitter, the electrical conductor, and the first pre-column fluid junction are housed in a replaceable cartridge. Example 8. The electrospray system of example 7, wherein the cartridge includes a high-voltage electrical connector that is electrically connected to the electrical conductor or to a current sensing circuit in series with the electrical conductor. Example 9. The electrospray system of example 8, wherein the current sensing circuit is housed in the replaceable cartridge. Example 10. The electrospray system of example 7, wherein the replaceable cartridge includes a housing that electrically shields the first pre-column fluid junction and the post-column fluid union. Example 11. The electrospray system of example 1, wherein a length of a fluidic path between the first pre-column fluid junction and the chromatographic column and a length of a fluidic path between the chromatographic column and the post-column fluid union are each less than 100 mm. Example 12. The electrospray system of example 1, further comprising a third pre-column fluid junction electrically connected to ground, the second pre-column fluid junction and the third pre-column fluid junction forming a pre-column voltage spacer. Example 13. A method for reducing electro-chromatographic effects in an electrospray system, comprising: flowing a fluid sample from a first pre-column fluid junction to a first end of a chromatographic column, the chromatographic column including a conductive or semi-conductive stationary phase disposed between the first end and a second end of the chromatographic column; separating analytes within the fluid sample using the chromatographic column; outputting the separated fluid sample from the second end of the chromatographic column to a first fluid port of a post-column fluid union, the post-column fluid union having a second fluid port connected to an electrospray emitter; and applying an equipotential voltage in a range of +1 to +10 kilovolts or in a range of −1 to −10 kilovolts at both the first pre-column fluid junction and at the post-column fluid union using an electrical conductor in electrical contact with the first pre-column fluid junction and the post-column fluid union. Example 14. The method of example 13, further comprising: applying a first voltage to a high side of a current sensing circuit using a power supply; and transmitting the equipotential voltage from a low side of the current sensing circuit to the electrical conductor. Example 15. The method of example 14, wherein the post-column fluid union and the first pre-column fluid junction are electrically connected in parallel with one another and in series with the current sensing circuit. Example 16. The method of example 13, wherein outputting the separated fluid sample from the second end of the chromatographic column to a first port of the post-column fluid union includes flowing the separated fluid sample through a fluidic path having an inner diameter of 30 micrometers or less to reduce peak broadening. Example 17. The method of example 13, wherein flowing the fluid sample from the first pre-column fluid junction to the first end of the chromatographic column includes flowing the fluid sample through a fluidic path having a length of less than 100 mm. Example 18. The method of example 13, wherein the chromatographic column, the post-column fluid union, the electrospray emitter, the electrical conductor, and the first pre-column fluid junction are housed in a replaceable cartridge, the method further comprising: connecting a second pre-column fluid junction of the cartridge to a source of the fluid sample; and flowing the fluid sample from the second pre-column fluid junction to the first pre-column fluid junction. Example 19. The method of example 18, wherein the cartridge includes a high-voltage electrical connector in electrical connection with the electrical conductor, the method further comprising: electrically connecting a power supply to the high-voltage electrical connector. Example 20. The method of example 14, wherein the first voltage is greater than the equipotential voltage. Example 21. A cartridge for insertion into an electrospray system, the cartridge comprising: a first pre-column fluid junction to receive a fluid sample; a chromatographic column for separating analytes within the fluid sample, the chromatographic column including a conductive or semi-conductive stationary phase disposed between a first end and a second end of the chromatographic column, the first end fluidically connected to the first pre-column fluid junction; a post-column fluid union having a first fluid port and a second fluid port, the first fluid port receiving separated analytes in the fluid sample from the second end of the chromatographic column; an electrospray emitter fluidically connected to the second fluid port; and an electrical conductor connected to the post-column fluid union and the first pre-column fluid junction to equalize electrical potential between the post-column fluid union and the first pre-column fluid junction. Advantages and features of the present disclosure can be further described by the following examples: